This invention relates to improvements in an air breather structure for an automatic transmission, the structure allowing a space defined by a housing to communicate with outside air so as to counterbalance atmospheric pressure differentials between the interior and exterior of the housing.
In an automatic transmission housing, oil is held for lubricating, cooling, and hydraulically actuating a transmission mechanism of the automatic transmission. The automatic transmission housing is generally configured by uniting a transmission case (that houses the transmission mechanism) and an extension case (that houses a parking gear), and additionally is formed to have an air breather structure that allows a communication between a space in the housing and outside air. Atmospheric pressure differentials between the interior and exterior of the housing, attended with oil's comings and goings or temperature variations in the automatic transmission, are counterbalanced by virtue of the air breather structure through which air passes out of or into the housing.
Such an air breather structure is disclosed by the present inventor in Japanese Patent Provisional Publication No. 10-103453, in which a bulkhead part dividing the automatic transmission housing into transmission case-side and extension case-side spaces is formed with a through hole at its upper end section, the through hole establishing a communication between the transmission case-side and extension case-side spaces. The upper end section of the bulkhead part is formed further with a hollow open to the extension case-side space. The hollow is covered with a lid member, thereby constituting an oil drop separation chamber, i.e. a breather chamber.
The breather chamber is arranged to communicate with the outside of the transmission case through a vent defined at a relatively upper portion of the breather chamber, while arranged to communicate with the extension case-side space through two groove structures disposed vertically apart from each other.
With the through hole, internal pressures of the transmission case-side and extension case-side spaces are counterbalanced. Further, the breather structure has upper and lower groove structures as discussed above, and therefore, even if one groove structure is temporarily obstructed by oil such as at vehicle inclination, the other groove structure ensures the communication with the extension case-side space thereby counterbalancing the atmospheric pressure differentials between the interior and exterior of the automatic transmission housing.